Bromination process

ABSTRACT

This invention relates to a novel process which comprises feeding a mixture formed from diphenylethane and bromine to a stirrable reaction mass comprised of bromine and a bromination catalyst to yield a decabromodiphenylethane wet cake which can be most economically treated to provide a high quality decabromodiphenylethane product.

REFERENCE TO RELATED APPLICATIONS

This application is a continuation of commonly-owned application Ser.No. 10/445,554, filed May 27, 2003, now U.S. Pat. No. 6,768,033, whichis continuation of commonly-owned copending application Ser. No.10/225,951, filed Aug. 21, 2002 now U.S. Pat. No. 6,603,049, issued Aug.5, 2003 (the disclosure of which is incorporated herein by reference),which is a continuation of commonly-owned application Ser. No.08/658,983, filed Jun. 4, 1996, now U.S. Pat. No. 6,518,468 B1 issueFeb. 11, 2003, which is a continuation of commonly-owned applicationSer. No. 08/338,711, filed Nov. 14, 1994, now abandoned, which in turnis a continuation-i -part of commonly-owned application Ser. No.08/317,792, filed Sep. 16, 1994, now abandoned.

BACKGROUND OF THE INVENTION

This invention relates to an improved process for the bromination ofdiphenylalkanes.

Brominated diphenylalkanes, e.g., decabromodiphenylethane, are knownflame retardants for use in polystyrene and polyolefin-basedthermoplastic formulations. It is predicted that decabromodiphenylethanewill soon become one of the major flame retardants used by thethermoplastic industry. In response to this market opportunity, severaldecabromodiphenylethane processes have been proposed. See U.S. Pat. Nos.5,077,334, 5,008,477 and 5,030,778.

While these processes are quite efficacious, there is always a desire todevelop more economical and technologically beneficent processes. It isan object of this invention to provide such a process.

THE INVENTION

This invention provides a unique process for producing an intermediatedecabromodiphenylethane slurry from which a decabromodiphenylethane wetcake can be more efficiently obtained. Even further, the obtained wetcake is most easily convertible to a high-quality ready-to-useflame-retardant product. The wet cake is characterized by having a loweroccluded bromine content than that which is obtainable by priorprocesses.

The process of this invention comprises: mixing bromine anddiphenylethane, the molar ratio of bromine to diphenylethane beinggreater than about 5:1, but preferably less than about 30:1; and quicklyfeeding the resultant mix to a stirrable reaction mass comprisingbromine and a bromination catalyst to yield decabromodiphenylethane.

It is theorized, though this invention is not to be limited to aparticular theory, that the feeding of the bromine/diphenylethanederived mixture (which mixture is very dilute in diphenylethane and/orunderbrominated diphenylethane) to the reaction mass favorably affectsthe crystallization of the decabromodiphenylethane product in thereaction mass so that there is a reduction in the formation of extremelysmall particles (fines) and so that there is an attenuation of theoccluded free bromine content in the crystalline structure. It isbelieved that by having the bromine present in diluent quantities, asthe derived mixture is fed, there is obtained, in the area of the feed,(1) a minimization of the variability of the brominated diphenylethaneconcentration, and (2) the unlikelihood that the crystallization medium,i e., the reaction mass, will become excessively supersaturated withdecabromodiphenylethane. Thus, good, slowed crystal growth is promotedand crystal nucleation is abated.

In addition, the diluent function of the fed bromine benefits productcolor. It is theorized that when the derived mixture is fed to thereaction mass there is a transient feed plume formed in the reactionmass. There, the diluent bromine acts as a mass transfer impediment toimpede the bromination catalyst contained in the reaction mass fromreaching some of the yet to be brominated or underbrominateddiphenylethane located in the plume. This is beneficial since it isbelieved that the bromination catalyst will attack, i e., cleave, thediphenylethane —C—C— bridge if there is insufficient or no brominationof the diphenylethane prior to contact with the catalyst. The cleavedmaterials are, in many instances, undesirable color bodies. By impedingthe mass transfer of the catalyst, for even a very short period of time,more diphenylethane will have sufficient time to obtain the degree ofbromination needed to deter cleavage. Once the plume is dissipated inthe reaction mass, and this occurs quickly, the bromination catalyst canthen effectively catalyze the reaction to obtain the desiredar-brominated decabromodiphenylethane product.

In addition to diminishing —C—C— cleavage, the dilution effect favorablyaffects the formation of color bodies by reducing the concentration ofbromination loci per unit volume. Since the bromination loci areexothermic, the reduction in their concentration enables the avoidanceof obtaining color body producing degradation temperatures at eachindividual locus. The large amount of bromine around each reaction locusacts as heat sink so that the heat is effectively dissipated.

Generally speaking, the processes of this invention will be most usefulto the commercial decabromodiphenylethane producer who deals with largereaction volumes, say larger than about 1,000 L (250 gal). Mostcommercial reactions will be sized from this minimum up to about 32,000L (8,000 gal). It is in dealing with large reaction masses where theproblems associated with decabromodiphenylethane production are mosteasily seen as mass transfer and crystallization quality are moreproblematic.

DESCRIPTION OF THE DRAWING

FIG. 1 is a cross-sectional, partial view of a mixer suitable for use inthe practice of this invention.

DETAILED DESCRIPTION

The diphenylethane reactant has the formula:

and has the IUPAC name, 1,2-diphenylethane. For convenience, thiscompound will be simply referred to as diphenylethane.

The diphenylethane can be produced by various routes. For example, CA 973865d (Japanese Kokai 82/45114) and CA 46 7084g disclose the reaction ofbenzene and ethylene dihalide in the presence of aluminum trichloride toyield diphenylethane.

It is not uncommon for the diphenylethane to contain impurities,especially isomeric impurities, e.g., 1,1-diphenylethane. Since suchimpurities can adversely affect the color of the decabromodiphenylethaneproduct, it is desirable to reduce the impurity level. Such can be doneby the use of conventional purification processes, such asrecrystallization wherein the diphenylethane is dissolved in a solventand recrystallized one or more times until the purity level sought isachieved.

The diphenylethane used in forming the bromine/diphenylethane derivedmixture is preferably provided as a molten liquid due to the ease offorming an intimate mix with the bromine. To obtain the molten state,the diphenylethane is brought to a temperature which is in excess of itsmelting point (53° C. to 55° C./127° F. to 131° F.). Preferably, thetemperature is within the range of from about 55° C. to about 80° C.(130 to 175° F.). The higher temperatures are preferred as the viscosityof the molten diphenylethane will be lower and thus facilitate theformation of the derived mixture. Most preferred is a temperature withinthe range of from about 70° C. to about 80° C. (160 to 175° F.).

Until it is used, it is preferred that the molten diphenylethane beblanketed by a non-oxidizing atmosphere. Such an atmosphere can beprovided by most inert gases, for example, nitrogen, argon, neon,helium, krypton, xenon and the like. By providing the inert atmosphere,it has been found that the color characteristics of the finaldecabromodiphenylethane product are benefitted. It is theorized thatthis color benefit is a result of preventing or at least reducing theproduction of oxidation decomposition impurities in the moltendiphenylethane. The decomposition impurities are probably1-hydroxy-1,2-diphenylethane, benzaldehyde, benzyl alcohols and thelike.

The bromine/diphenylethane derived mixture can also be formed by addingsolid diphenylethane to the diluent bromine.

It is preferred that the bromine used in the processes of this inventionbe essentially anhydrous, i.e., contain less than 100 ppm water, andcontain no more than 10 ppm organic impurities, e.g., oil, grease,carbonyl containing hydrocarbons, iron, and the like. With such abromine purity, there is little, if any, impact on the color attributesof the decabromodiphenylethane product. Available, commercial gradebromine may have such a purity. If, however, such is not available, theorganic impurities and water content of the bromine can be convenientlyreduced by mixing together a 3 to 1 volume ratio of bromine andconcentrated (94-98 percent) sulfuric acid. A two-phase mix is formedwhich is stirred for 10-16 hours. After stirring and settling, thesulfuric acid phase, along with the impurities and water, is separatedfrom the bromine phase. To further enhance the purity of the bromine,the recovered bromine phase can be subjected to distillation.

The formation of the derived mixture from liquid bromine and moltendiphenylethane can be accomplished by most any conventional techniquefor mixing two liquids. A most preferred technique is to form themixture in a flow or line mixer to which the bromine and diphenylethaneare fed. Exemplary of such mixers are, (1)jet mixers which depend uponthe impingement of one stream into another stream, (2) injectors inwhich one liquid flow induces another liquid flow, (3) orifices andmixing nozzles in which the pressure drop is used to effect the mixing,(4) valves, and (5) pumps, especially centrifugal pumps into which thetwo streams are fed to the suction side. A common characteristic ofthese preferred mixers is that the mixing occurs quickly and thoroughly.

FIG. 1 depicts a particularly preferred jet mixer for use in the processof this invention. The jet mixer, generally designated by the numeral10, provides a longitudinal, axially directed conduit 12 through whichthe liquid diphenylethane flows. Conduit 14 carries the bromine to anannular space 24 which surrounds conduit 12. Spacers 20, 20 ^(a), 22 and22 ^(a) locate and hold conduit 14 in position with respect to annularspace 24. At the lowermost extent of annular space 24 there is radialconduit 26 which directs the bromine flow in an inward and radialdirection with respect to the long axis of conduit 12. Adjacentdiphenylethane discharge port 17 and radial conduit 26 is impingementchamber 16. Downstream from impingement chamber 16 is mixing chamber 18and mixture discharge port 19.

In operation, bromine flows through conduit 14, annular space 24 andradial conduit 26 to reach impingement chamber 16. At impingementchamber 16 the bromine is traveling in an inward and radial direction.The diphenylethane flows down conduit 12 and through discharge port 17in an axial direction with respect to impingement chamber 16. The thusflowing diphenylethane intersects and impinges perpendicularly with theflowing bromine from radial conduit 26. Subsequent to the impingement,the resulting mix flows into mixing chamber 18 and is then dischargedwith velocity as a stream from the mixer.

The mixer dimensions determine the velocity of the stream from the mixerand the residency time of the bromine/diphenylethane derived mix in themixer. For any desired velocity and residency time, these dimensions canbe conventionally determined. For example, on a commercial scale, for a272 kg/hr (600 lb/hr) molten diphenylethane and a 2,400 kg/hr (5,300lb/hr) bromine feed rate and for a mixer residency time of about 0.01second. The height of radial conduit 26 can be 0.635 cm (¼ inch) whilemixing chamber 18 can be 0.80 cm ( 5/16 inch) in diameter and 1.9 cm (¾inch) long.

In those cases where the derived mixture is made from liquid bromine andsolid diphenylethane, conventional liquid-solid mixing systems can beused, understanding that as the diphenylethane dissolves in the bromineit will begin to be brominated.

Subsequent to the formation of the bromine/diphenylethane derivedmixture, it is preferred that the mixture be quickly fed to the reactionmass. Most preferably, the mixture is fed to the reaction mass withinabout 2 seconds of its formation. Generally, the time which elapsesbetween the mixture formation and its being fed will be less than about0.05 seconds. A preferred time is within the range of from about 0.001to about 0.05 seconds and a most preferred range is from about 0.005 toabout 0.01 seconds. The preferred and most preferred ranges are mostsuitable when the mixing device used to form the mixture is compromisedby the evolution of the HBr gas due to the reaction of thediphenylethane and bromine.

The molar ratio of bromine to diphenylethane used to form the desiredmixture lies within the range of from about 5:1 to about 30:1, andpreferably within the range of from about 7.5:1 to about 25:1. Mostpreferably, the molar ratio lies within the range of from about 9:1 toabout 25:1. Most highly preferred is a ratio within the range of about1:1 to 15:1. Molar ratios in excess of 30:1 may be used; however, suchexcess ratios will result in more liquid bromine being present after thereaction and thus, higher attendant costs for the bromine recovery step.

The derived mixture will be comprised of bromine, and one or more ofdiphenylethane, mono-, di-, tri- and tetrabromodiphenylethane. The exactcomposition of the derived mixture before it is fed to the reaction masswill depend upon the time that has lapsed between the formation of themixture and its feed to the reaction mass. The more brominated specieswill be present in larger quantities as the time period increases sincethere will be sufficient time for the additional bromination to occur.In those cases where the time period is short, the derived mixture willcontain more diphenylethane and/or the lower brominated species.

It is to be understood that it is permissible to have present in thederived mixture components other than bromine, diphenylethane andbrominated diphenylethane provided that these components do not defeatthe very reason for practicing the processes of this invention. Forexample, it is best that the derived mixture not contain a brominationcatalyst as such catalyst can cause the above discussed —C—C— cleavagein the unprotected species. However, if the practitioner wishes to use abromine recycle stream from a previous process run, then it is possiblethat the recycled bromine could contain some small concentration of astill active bromination catalyst. Considering the small amount ofcatalyst present, the use of such recycled bromine would be permissibleas the deleterious impact of the catalyst, if any, would be so small asto be acceptable in view of the effect sought.

The bromine temperature should be sufficiently high so that when moltendiphenylethane is used it is not cooled to form a solid. For most allcases, the bromine temperature is preferably within the range of fromabout 30° C. to about 75° C.

In commercial systems process efficiency is paramount. Thus, the feedrate of the derived mixture should be as high as is possible in view ofthe capacity of the reaction system to handle evolved HBr. The feedstream cross sectional area/velocity are selected so as to expend asmuch energy as possible in the mixing process. It has been found thatsmaller cross sectional areas and faster feed stream velocities willgenerally yield larger crystals, lower occluded bromine in the productand a better colored product. There are practical limits, however, andthey are set by cost and benefit balances and available equipment, e.g.,feed pumps and overhead capacity. Exemplifying suitable cross sectionalareas and velocities are: the areas within the range of from about 0.03to about 10 cm² (0.0005 to 1.6 inches²) and the velocities within therange of from about 0.3 to about 30 m/sec (0.98 to 98 ft/sec). Suchranges are suitable for most stirred commercial reactors, and areespecially suitable for 1000 to about 30,000 L (260 to about 8000 gal)reaction masses, all having the appropriate overhead capacities tohandle and separate evolved Br₂ and HBr from their respective reactionmasses. Preferred are cross sectional areas within the range from about0.5 to about 2 cm² (0.08 to 0.31 inches²) and velocities within therange of from about 5 to about 10 m/sec (16.4 to 32.8 ft/sec).

The derived mixture can be fed by using one or more feed streams. Inthose cases where there are a plurality of streams, each stream isproportioned to handle its fraction of the feed service.

The derived mixture feed stream can be introduced into the reactoreither above or below the surface of the reaction mass. It is preferredthat the introduction occur below the surface, say from about 2.5 cm (1inches) to about 60 cm (24 inches) for a commercial scale reactor. Ifabove-surface feed is used, then the point of introduction willpreferably be near the surface to prevent splattering.

The reactor to which the derived mixture is fed will generally be anagitated, glass-lined reactor to which has already been charged bromineand bromination catalyst.

The charged bromination catalyst is preferably AlCl₃ and/or AlBr₃,although use may be made of aluminum powder, iron powder, FeCl₃ andFeBr₃, alone or in combination with the aluminum trihalides. Otherbromination catalysts are suitable provided that they have sufficientcatalytic activity to provide for the ar-perbromination needed to yielda decabromodiphenylethane product. Catalytic quantities are used.Typically, the catalysts will be present in an amount within the rangeof from about 0.1 to about 20 weight percent, based on the weight of thediphenylethane fed. The amount used will generally depend on thecatalytic activity of the chosen catalyst, reaction temperature, and theamount of bromine used. A preferred amount is within the range of fromabout 2 to about 15 weight percent on the same basis. When AlCl₃ is thecatalyst, for example, from about 5.0 to about 7.0 weight percent willbe most preferred.

The bromination catalyst and bromine can be charged to the reactionvessel in any order or together. After charging, the bromine/catalystmix will preferably be brought to a temperature within the range ofabout 50° C. to about 60° C. (122 to 140° F.). Lower or highertemperatures are possible, but lower temperatures may result in lowerbromination while higher temperatures will require pressurizedoperation.

The amount of bromine in the reaction mass during the feed of thederived mixture is that amount which is sufficient to yield a stirrablereaction mass and, ultimately, a decabromodiphenylethane product (such aproduct is defined as a mixture of brominated diphenylethanes having anaverage bromine number of at least about 9.0 and preferably within therange of from about 9.5 and 10). There are two sources of bromine whichwill contribute bromine to the reaction mass—the bromine whichaccompanies the derived mixture and the bromine which is initiallypresent in the reactor before the feed. The amount of bromine initiallypresent in the reactor is preferably within the range of from about 25to about 150% of the stoichiometric amount needed to produce thediphenylethane product. Most preferred is an initial bromine amountwhich is within the range of from about 75% to about 100% of thestoichiometric amount.

The total amount of bromine, that is the sum of the amount of initialbromine in the reactor and the amount of bromine used in forming thebromine derived mixture, will provide a molar ratio of bromine to thediphenylethane used which is within the range of from about 14:1 toabout 30:1. Preferred is a molar ratio of from about 16:1 to about 24:1and most preferred is a molar ratio of from about 18:1 to about 20:1.

During the feed of the bromine/diphenylethane derived mixture, thereaction mass temperature is kept within the range of from about 30° C.to about 80° C., and preferably within the range of from about 50° C. toabout 60° C. Since the bromination of diphenylethane is exothermic,cooling of the reaction mass is needed to maintain the reaction masstemperature chosen. The heat of reaction can be removed from thereaction mass by cooling the reaction vessel or by having the reactionmass under reflux conditions so that heat can be removed by the use ofan overhead condenser.

It is preferred that the pressure in the reaction vessel be that whichprovides a refluxing condition at the selected reaction masstemperature. With a refluxing condition, control of the reaction masstemperature is facilitated. If temperature control is effectedotherwise, i.e., by the use of heating or cooling jackets, then thepressure can be any which is not prohibitive of the obtainment of thevarious defined parameters of the process. Also, since temperaturesabove the boiling point of bromine are useful in the process of thisinvention, super atmospheric pressures, e.g., 15 psig can be used toobtain same.

The process of this invention is benefitted by the fact that, after thefeed of the derived mixture feed to the reactor is completed, no furtherlengthy maintenance of the formed reaction mass is needed to completethe bromination reaction to obtain the decabromodiphenylethane product.The bromination reaction after the feed has been completed is bestmonitored by detecting HBr evolution from the reaction mass. Cessationof HBr evolution signals the end of the bromination reaction. With theprocess of this invention the bromination reaction is usually finishedwithin one minute of the cessation of the derived mixture feed. Thus,product recovery can occur quite soon after the derived mixture feed iscompleted. It is to be understood that the practitioner can wait forsome time to recover the product as no harm is done except that processcycle time is extended.

After the bromination reaction has at least substantially ceased, thereaction mass will comprise a liquid solid mixture. The solid comprisesa precipitate which includes decabromodiphenylethane product, occludedfree bromine and other impurities. The liquid will comprise mostlybromine and catalyst. Before recovering the solid, it is preferred tofirst deactivate the catalyst. Deactivation can be accomplished byintroducing water to the reaction mass or vice versa. Generally, it ispreferred to move the reaction mass from the reactor to a strippingvessel. The stripping vessel will contain water which (1) deactivatesthe catalyst and (2) which will provide for the formation of a slurryafter the bromine is stripped off.

Once in the stripping vessel, the reaction mass, which comprises thesolids and the bromine, forms one phase and the water, the other phase.The water phase is on top. The vessels contents are heated to boil-offor strip the bromine. The stripping temperature is generally around 57°C. (135° F.). The bromine boils off and passes through the water phaseand takes a small amount of water with it. As more bromine is stripped,the solids and bromine phase begins to thicken. At the point where thereis approximately an equal weight of bromine and solids, the solids willbegin to transit into the water phase. As more bromine is stripped, theremaining solids will slurry with the water. The solids, principallydecabromodiphenylethane product, do not wet well in water. The largerdecabromodiphenylethane product particles tend to settle in the water.The fines, and there are always some, do not, for the most part, settle,but instead move to the top of the water surface and form a froth. Themore fines, the worse the froth formation and the slower the strippingmust proceed. Since the practice of the process of this inventionresults in an abatement of the fines production, there is an attendantreduction in froth production. Thus, it is possible, with the practiceof this invention, to use a higher stripping rate. Increases instripping rates of up to 100% have been experienced by the practice ofthis invention.

After the bromine has been stripped off, the water and solids slurry istreated with an aqueous base to neutralize any HBr present. The aqueousbase can be any suitable base, e.g., an aqueous solution of NaOH orNa₂CO₃.

After the neutralization step, the slurry in the stripper vessel isremoved therefrom and is processed to separate the liquid portion fromthe solids portion. This is most easily accomplished by centrifuging. Itis at this centrifuging step that another process benefit is realizeddue to the reduction of fines production. When a large quantity of finesare present, the centrifuging time is substantially lengthened as thefines interfere with the separating movement of water from the solidsportion of the slurry. By having a low fines production, there has beenseen a 50-60% reduction in centrifugation times.

The undried solids recovered from the slurry are referred to herein bythe term “wet cake”. This term is not meant to be restricted by anyparticular manner of solids recovery and/or by ancillary treatments ofthe slurry or recovered solids, e.g., neutralization, washing and thelike. Most often the wet cake is recovered from the filter media as acake-like material.

The wet cakes obtained in accordance with this invention are unique inthat they have a relatively low occluded free bromine content, say fromabout 500 ppm to about 2000 ppm and most probably from about 900 ppm toabout 1200 ppm. Compare wet cakes having a high, e.g., 3500 ppm,occluded free bromine content and which are produced by processes whichdo not use highly diluted diphenylethane feeds. These wet cakes have ahigh, e.g., 3500 ppm, occluded free bromine content.

The term “occluded free bromine” refers to that bromine which is tightlyheld by the recovered decabromodiphenylethane product component of thewet cake so that ordinary washing techniques are insufficient to reduceits content in the product.

The wet cake is preferably submitted to a dry and grind technique, suchas that provided by a hammer mill, e.g., Raymond Mill. The combinationof drying and grinding yields a dry powder of reduced average particlesize and reduced occluded free bromine content. Preferred dryingtemperatures are within the range of from about 150 to about 350° C.(302 to 662° F.). The grinding is preferably designed to reduce theaverage particle size of the decabromodiphenylethane product to bewithin a range of from about 3 to about 5 microns. Both of the above dryand grind conditions can be obtained by the use of a hammer mill. Insome instances, it may be preferred that the heating occur prior to thegrinding step; however, the reverse order is usable and functional.After the grind and dry step the resultant dry decabromodiphenylethaneproduct will still contain some occluded free bromine. In these cases,and that will be the case in most situations, the product will stillcontain 700 to 1000 ppm occluded free bromine. This level still exceedsthe more acceptable and desired occluded free bromine level of 150 to200 ppm occluded free bromine.

The color of a wet cakes also evidences its occluded free brominecontent. Compare a Yellowness Index (YI), as measured by ASTM D-1925, ofabout 24 for the dried and ground wet cakes produced with undilutedmolten diphenylethane against a YI of from about 12 to about 18 fordried and ground wet cakes of this invention.

To further reduce the occluded free bromine content of the ground anddried product so as to obtain the acceptable level, the product isoven-aged at a temperature within the range of from about 175° C. toabout 290° C. (350° F. to about 550° F.) for about 1 to about 20 hours.The higher temperatures use the shorter heating times while the lowertemperatures need the longer heating times. A preferred temperaturerange is from about 230 to about 260° C. (446 to 500° F.). With thesepreferred temperatures, the oven-aging time is from about 3 to about 9hours. A comparison against decabromodiphenylethane processes which useundiluted molten diphenylethane feeds, shows that such processes needlonger aging times, 6 to 20 hours, at comparable temperatures, to obtainthe same level of occluded free bromine in the final product.

The oven-aging produces the final decabromodiphenylethane product whichwill, preferably, be principally comprised of at least about 90 wt %(and more preferably from about 95 wt % to about 99.8 wt %) ofdecabromodiphenylethane and smaller amounts of nonabromodiphenylethane,octabromodiphenylethane, and decabromostilbene with an occluded freebromine content within the range of from about 100 ppm to about 300 ppm.

The decabromodiphenylethane product of this invention may be used as aflame retardant in formulation with virtually any flammable material.The material may be macromolecular, for example, a cellulosic materialor a polymer. Illustrative polymers are: olefin polymers, cross-linkedand otherwise, for example, homopolymers of ethylene, propylene, andbutylene; copolymers of two or more of such alkylene monomers andcopolymers of one or more of such alkylene monomers and any othercopolymerizable monomers, for example, ethylene/propylene copolymers,ethylene/ethyl acrylate copolymers and ethylene/vinyl acetatecopolymers; polymers of olefinically unsaturated monomers, for example,polystyrene, e.g., high impact polystyrene, and styrene copolymers;polyurethanes; polyamides; polyimides; polycarbonates; polyethers;acrylic resins; polyesters, especially poly(ethyleneterephthalate) andpoly(butyleneterephthalate); epoxy resins; alkyds; phenolics;elastomers, for example, butadiene/styrene copolymers and butadiene/acrylonitrile copolymers; terpolymers of acrylonitrile, butadiene andstyrene; natural rubber; butyl rubber; and polysiloxanes. The polymermay also be a blend of various polymers. Further, the polymer may be,where appropriate, cross-linked by chemical means or by irradiation.

The amount of decabromodiphenylethane product used in a formulation willbe that quantity needed to obtain the flame retardancy sought. It willbe apparent to the practitioner that for all cases no single precisevalue for the proportion of the product in the formulation can be givensince this proportion will vary with the particular flammable material,the presence of other additives and the degree of flame retardancysought in any given application. Further, the proportion necessary toachieve a given flame retardancy in a particular formulation will dependupon the shape of the article into which the formulation is to be made,for example, electrical insulation, tubing and film will each behavedifferently. In general, however, the formulation may contain from 5 to40 weight percent, preferably 10 to 30 weight percent, of the productwhen it is the only flame retardant compound in the formulation.

It is especially advantageous to use the flame retardant final productof this invention with an inorganic compound, especially ferric oxide,zinc oxide, zinc borate, the oxide of a Group V element, for example,bismuth, arsenic, phosphorus and especially antimony, in theformulation. Of these compounds, antimony oxide is especially preferred.If such a compound is present in the formulation, the quantity ofproduct needed to achieve a given flame-retardancy is accordinglyreduced. Generally, the product and the inorganic compound are in aweight ratio of from 1:1 to 7:1, and preferably of from 2:1 to 4:1.

Formulations containing a flame retardant system comprised of theproduct of this invention and the above inorganic compounds may containup to about 40 percent by weight of the system and preferably between 20percent and 30 percent by weight.

Any of the additives usually present in formulations, e.g. plasticizers,antioxidants, fillers, pigments, and UV stabilizers can be used informulation with the product of this invention.

Thermoplastic articles formed from formulations containing athermoplastic polymer and a product of this invention can be producedconventionally, e.g., by injection molding, extrusion molding,compression molding, and the like.

The following Examples merely illustrate the invention described hereinand are not to be taken as limiting such inventions.

EXAMPLE I

To a 15,140 L (4,000 gal) glass lined agitated reactor is added 12,712kg (28,000 lb) of bromine. The agitator was then started and 68 kg (150lb) AlCl₃ was added. The reaction content was heated to 58° C. (135°F.).

Bromine flow through a mixer was established at 2,406 kg/hr (5300lb/hr). A bromine heater was used to obtain a temperature for thebromine of between 50° C. and 55° C. (120° F. and 130° F.). Moltendiphenylethane flow to the mixer was then established at 272 kg/hr (600lb/hr).

The mixer was located at the end of a dip tube which extended to a point60 cm (24 inches) beneath the reaction mass surface. The mixer was ofthe type shown in FIG. 1 hereof. The mixer was designed to handle 272kg/hr (600 lb/hr) diphenylethane and 2406 kg/hr (5300 lb/hr) bromine.The mixer forced the bromine radially inward into a 0.48 cm ( 3/16 inch)stream of diphenylethane. The mixer provides a mixing chamber throughwhich the resultant intimate mix then passes. The chamber had a 0.8 cm (5/16 inch) diameter and was 1.9 cm (¾ inch) long. The stream leaving themixer had a diameter of about 0.8 cm ( 5/16 inch) and a velocity ofabout 6.1 m/sec (20 ft/sec).

The reaction mass temperature rose to reflux temperature, which wasabout 60° C. (140° F.), at a reaction pressure of 2.05×105 PA (15 psig).

The diphenylethane and bromine were allowed to flow until 1090 kg (2400lb) of diphenylethane had been fed. Subsequently, the diphenylethaneflow was stopped and nitrogen was blown through the diphenylethanepassages. The bromine flow was stopped and nitrogen was blown throughits passages.

The reaction mass was transferred to a stripping vessel to which hadbeen previously added 6000 L (1500 gal) of water. The resulting mix wasthen heated and stirred to a temperature of about 58° C. (135° F.) so asto obtain the boil-off of the bromine. A 1% aqueous solution ofAerosol™-OTB made by American Cyanamide was used as a wetting agent. Theboil-off period lasted about 4 hours.

After the boil-off, the remaining solids and water slurry was treatedwith a base to neutralize and acidic components. The neutralized slurrywas fed over a 2.5 hour period to a centrifuge to yield a wet cake. Thewet cake was then recovered and fed to a Raymond Mill wherein the wetcake was dried and ground. The wet cake was dried at a temperature of205° C. (400° F.) for a period of 2 seconds and ground to an averageparticle size of from about 80 to about 4.5 microns.

The foregoing procedure was repeated several times except that in threeof the runs, 23-26 minutes was used to get the bromine flow andtemperature established. In another run, 4 minutes was used.

Comparative runs were made in which the diphenylethane was fed to thereactor alone.

Comparative Runs

To a 15,140 L (4,000 gal) glass lined agitated reactor was added 21,760kg (48,000 lb) of bromine. The agitator was then started and 68 kg (150lb) AlCl₃ was added. The reactor contents were heated to 58° C. (135°F.).

Molten diphenylethane flow to a dip tube was then established at 272kg/hr (600 lb/hr). The dip tube extended to a point 120 cm (48 inches)beneath the reaction mass surface.

The diphenylethane was allowed to flow until 1089 kg (2400 lb)diphenylethane had been fed. Subsequently, the diphenylethane flow wasstopped and nitrogen was blown through the diphenylethane dip tube.

The reaction mass was transferred to a stripping vessel to which hadbeen previously added 6000 L (1500 gal) of water. The resulting mix wasthen heated and stirred to a temperature of about 58° C. (135° F.) so asto obtain the boil-off of the bromine. A 1% aqueous solution ofAerosol™-OTB made by American Cyanamide was used as a wetting agent. Theboil-off period lasted about 8 hours.

After the boil-off, the remaining solids and water slurry was treatedwith a base to neutralize and acidic components. The neutralized slurrywas fed over a 5 hour period to a centrifuge to yield a wet cake. Thewet cake was then recovered and fed to a Raymond Mill wherein the wetcake was dried and ground. The wet cake was dried at a temperature of205° C. (400° F.) for a period of 2 seconds and ground to an averageparticle size of from about 80 to about 4.5 microns.

Measurements were obtained from all of the runs for (1) the bromineboil-off rate, (2) the centrifugation rate, (3) the occludedfree-bromine content of the wet cake before and after Raymond Milling,and (4) the color values of the Raymond Milled product.

Using the process of this invention resulted in an average 75% increasein the boil-off rate and an average 97% increase in the centrifugationrate. The wet cake from the comparative runs had, on average, 78% (8samples, 2,007 to 5,463 ppm, avg. 3,773 ppm occluded Br₂) more occludedfree bromine than did the wet cakes produced by the process of thisinvention (8 samples, 1,308 to 838 ppm, avg. 1,122 ppm occluded Br₂).After Raymond Milling, the occluded free bromine content of thecomparatively dried and ground products was, on average, 225% higherthan for the dried and ground products of this invention. Compare, forthe comparative 8 samples, 1,331 to 4,771 ppm, avg. 3,117 ppm occludedBr₂ and for the dried and ground products of this invention, 8 samples,499 to 1232 ppm, avg. 890 ppm occluded Br₂. Based upon the YellownessIndex (YI), the Raymond Milled products of this invention have a bettercolor than the comparative products. The YI values, ASTM D-1925, for thedried and milled material produced in accordance with this invention,prior to oven-aging, lie within the range of from about 12.5 to about17.5 whereas the comparative samples have a YI between about 22 to about26.

1. A process for bromination of diphenylethane, which process comprises:a) forming a mixture of at least bromine and molten diphenylethane; andb) feeding said mixture into a stirrable reaction mass comprisingbromine and a bromination catalyst to form a decabromodiphenylethaneproduct; wherein said catalyst is present in an amount within the rangeof from about 0.1 to about 20 weight percent, based on the weight ofsaid diphenylethane.
 2. A process according to claim 1 wherein saidamount of catalyst is within the range of from about 2 to about 15weight percent based on the weight of said diphenylethane.
 3. A processaccording to claim 1 wherein said amount of catalyst is within the rangeof from about 5 to about 7 weight percent based on the weight of saiddiphenylethane.
 4. A process according to claim 1 wherein said catalystused is selected from AlCl₃, AlBr₃ and a mixture thereof.
 5. A processaccording to claim 1 wherein said catalyst used is selected fromaluminum powder, iron powder, FeCl₃ and FeBr₃.
 6. A process according toclaim 5 wherein said catalyst is used in combination with AlCl₃ and/orAlBr₃.
 7. A process according to claim 1 wherein said mixture is fedbelow the surface of said reaction mass.
 8. A process according to claim1 further comprising: c) recovering as a wet cake,decabromodiphenylethane product formed in b); and d) drying and grindingsaid wet cake and/or said decabromodiphenylethane product; wherein saiddried and ground wet cake and/or said dried and grounddecabromodiphenylethane product exhibits a Yellowness Index (YI), asmeasured by ASTM D-1925, in the range of from about 12 to about
 18. 9. Aprocess according to claim 8 further comprising oven-aging said driedand ground wet cake and/or said dried and ground decabromodiphenylethaneproduct at a temperature within the range of from about 175° C. to about290° C. for a heating time of from about 1 to about 20 hours.
 10. Aprocess according to claim 9 wherein said temperature is within therange of from about 230° C. to about 260° C. and said heating time isfrom about 3 to about 9 hours.